Field of the Invention
The present invention relates to a numerical controller, and in particular, relates to a numerical controller which enables optimum speed control in accordance with a shape of a movement path.
Description of the Related Art
In control of a machine by a numerical controller, allowable accelerations are generally set with respect to axes included in the machine. In a case where a driving target is moved along a movement path of a curved shape and a corner shape, control is performed such that movement occurs at the highest speed within a range in which an acceleration does not exceed the allowable acceleration when the movement direction is changed.
FIG. 7 is a diagram for illustrating an example of conventional speed control in consideration of the allowable acceleration.
When the driving target such as a tool included in the machine is being moved at a movement speed v along a movement path indicated by the solid arrows, accelerations axn and ayn have to be increased in the case where the speed v is increased in order to change the movement direction at point n along the movement path, where the acceleration in the X-axis direction is axn and the acceleration in the Y-axis direction is ayn at point n on the movement path. Nevertheless, the acceleration axn is restricted by the allowable acceleration of the X axis, and moreover, the acceleration ayn is restricted by the allowable acceleration of the Y axis. Therefore, as the movement speed v of the driving target, the highest speed is set within a range in which the accelerations axn and ayn needed for changing the movement direction at point n do not exceed the respective allowable accelerations of the axes.
Moreover, when the driving target of the machine is moved, the speed can be set to be constant regardless of the movement direction.
As a conventional technique regarding such speed control on a movement path of a curved shape and a corner shape, for example, Japanese Patent Application Laid-Open No. 2-219107 discloses a speed control method of determining the speed from a curvature on an arc-shaped movement path or from a normal direction acceleration thereon.
Moreover, in Japanese Patent Application Laid-Open No. 05-313729, there is known a technique of automatically determining a corner shape between blocks in performing numerical control to perform in-position check even when an exact stop instruction (G09) or the like is not instructed in a machining program. In this technique, a corner angle α formed between a unit vector of a first block and a unit vector of a second block is calculated, determination is made as to whether a corner error due to a servo control delay exceeds an allowable range on the basis of the calculated corner angle α, and when it is determined that the allowable range is exceeded, in-position check is instructed to be performed on data of the first block to keep within the allowable range.
In the numerical controller, as a value used for deriving the speed of the driving target in speed control, a constant value is set, such as a normal direction acceleration, an allowable inward turning amount in consideration of post-interpolation acceleration and deceleration, and an in-position width. When only one value can be set for each of such constant values, an operator has to confirm the movement path of the driving target before starting machining, and to set each constant value to meet the point at which deceleration is most needed on the movement path, that is, the point with the most severe condition. However, in the case of such configuration, there arises a problem of a decrease in the speed of the whole machining, which causes a long cycle time.
Moreover, when machining is performed using a machining program constituted of minute line segments, as shown in FIG. 8A and FIG. 8B, since even the same shapes result in different angles between blocks depending on the number of instruction points (three points in the example of FIG. 8A; four points in the example of FIG. 8B), there arises a problem of difficulty to determine the shape in excellent precision.